SiC (silicon carbide) is characterized as (i) excelling in heat resistance and mechanical strength, (ii) being resistant to radiation, (iii) being easily controllable for valence of electrons or holes by doping, and (iv) having a large forbidden band width. For reasons such as these, SiC is expected as a semiconductor material for next-generation power devices and high-frequency devices.
Unfortunately, a monocrystal SiC substrate is inherently likely to have crystal defects caused by heat, such as a basal plane dislocation, a screw dislocation, and a micropipe. Further, a monocrystal SiC substrate likely has grain boundaries arising from nucleation.
Thus, when an active layer made of monocrystal SiC is grown on a monocrystal SiC substrate by vapor phase growth method, which is currently the mainstream of SiC epitaxial growth processes, crystal defects and/or the like inherent in the monocrystal SiC substrate are problematically propagated to the active layer.
In view of this, Patent Literature 1, for example, discloses the following technique: A first epitaxial layer is formed on a monocrystal SiC by liquid phase growth method (LPE). Then, a second epitaxial layer is formed on the first epitaxial layer by CVD. This prevents propagation of micropipe defects from the SiC substrate.
Further, Patent Literatures 2 to 4 disclose a liquid phase growth method (hereinafter referred to as metastable solvent epitaxy, or MSE) by which a set of a monocrystal SiC substrate, a polycrystalline SiC substrate, and an extremely thin metal silicon melt interposed between them is heat-treated so that monocrystal SiC is epitaxially grown. The method disclosed in Patent Literatures 2 to 4 for growing monocrystal SiC has an advantage in that it not only allows for formation of highly flat monocrystal SiC in which occurrence of micropipe defects is prevented, but also achieves a high growth rate.